a) Field of the Invention
This invention relates to a process for synthesizing cellulose aminomethanate which has utility in the manufacture of cellulose films or fibers, particularly the manufacture of regenerated cellulose film.
b) History of the Prior Art
Cellulose xanthate, dissolved as viscose, has been utilized for many years in the manufacture of regenerated cellulose film which has particular utility as sausage casings. With the increase in environmental awareness, concerns have been raised to the environmental management of flammable and toxic reactants and by-products of the viscose manufacturing process. The rapidly escalating cost of by-product management, coupled with the intrinsic costs of additives, such as plasticizers, which are often necessary when utilizing viscose for regenerated cellulose films, has forced the regenerated cellulose industry to search for viable alternatives to current viscose manufacturing processes.
One alternative, which has more recently been the focus of research for possible replacement of the viscose process, particularly in the sausage casing industry, is the use of ammonia derivatives, such as urea, as precursors reacted with cellulose to form a soluble cellulose derivative. The use of such materials is preferable as by-products are easily managed and do not appear to represent significant environmental impact. U.S. Pat. Nos. 1,771,461; 2,134,825; and 2,129,708 comprise some of the early work in that technology, demonstrating that film products are obtainable that have utility. Though the final products formed showed potential for use as a film, it wasn't until U.S. Pat. No. 4,789,006 that a product was produced having a combination of properties that made it appropriate for use as sausage casings.
Various different terminology has been used to describe the products of cellulose and urea, such as cellulose aminoformates, cellulose carbamates, cellulose aminomethanoates and cellulose aminomethanates as adopted in U.S. Pat. No. 4,789,006. To deter further confusion, the products that are formed with cellulose and urea, as presented in the above patents and hereinafter, will be referred to as cellulose aminomethanates.
Even though a cellulose aminomethanate product can now be made which is suitable for use as a sausage casing, problems still exist in the manufacturing process occasioned by the difficulty of using prior art carriers and swelling agents, such as liquid ammonia, to obtain uniform distribution of the urea through the cellulose material prior to the formation of the cellulose aminomethanate. This need for uniform distribution of the urea is disclosed in U.S. Pat. No. 4,404,369 and other prior art.
It is an object of this invention to improve the distribution of urea throughout the cellulose structure prior to the formation of cellulose aminomethanate, without the use of very low temperature, liquid ammonia processing.
It is another object of this invention to provide an improved cellulose aminomethanate material having uniform distribution of aminomethanate substituent.
These objects and more are achieved by an improvement to the process for synthesizing cellulose aminomethanate which comprises slurrying cellulose in low concentrations of aqueous caustic solutions, in the presence of urea, and steeping the slurried mixture, at from about 2.degree. C. to about -15.degree. C., for a time sufficient to permit swelling of the cellulose and uniform distribution of the urea.
It was found that when the cellulose aminomethanate is manufactured from product prepared in accord with this process, it has a uniform distribution of urea throughout the cellulose at the molecular level and comprises a suitable product for manufacturing sausage casing.